Method of and device for producing bundles of hollow fibers

ABSTRACT

Disclosed is a method of and a device for producing bundles of hollow fibers such as used for dialysis. The device includes a guiding device for a continuous fiber which rotates in a plane. At least two groups of take-up elements are mounted on a conveyor. The conveyor is intermittently activated so that a group of take-up elements is placed in a working position in the range of movement of the guiding device, and a strand of a desired thickness is wound around the take-up elements. Thereafter, the conveyor is activated to discharge the first group together with the completed strand from the working position and place the subsequent empty group of take-up elements in the working position, without interruption of movement of the guiding device. During the winding-up of the subsequent strand, the completed strand is cut and wrapped into bundles.

BACKGROUND OF THE INVENTION

The present invention relates in general to processing of hollow fibers,and in particular to a method of producing bundles of hollow fibersarranged parallel to each other, in which at least one continuous hollowfiber is wrapped by means of a movable guiding device about at least twotake-up elements spaced apart from each other, so that a strand ofhollow fibers is wound around these take-up elements. This inventionrelates also to a device for carrying out this method and relates alsoto a bundle of crimpled or waved hollow fibers.

A method of the aforedescribed kind is known for example from the Germanpublication DE-OS No. 2,259,949. This prior art method is based on theapplication of flexible hollow fiber continuously wound on a coil orspindle, whereby the hollow fiber is taken off by a rotary guidingdevice and laid in four half shells arranged in pairs. The convex sidesof two half shells engage each other and are clamped together, and thetwo pairs of engaging half shells are aligned in a plane in such amanner that the clearance between the two pairs corresponds to thelength of the hollow fiber bundles.

This prior-art method, however, is unsuitable for making bundles offreshly spun hollow fibers, inasmuch as, after achieving the desiredthickness of the bundle, the wrapping of the continuous fiber must beinterrupted so long until a set of empty half shells is brought into theworking position and fixed. Moreover, this known method permits theproduction of two partial bundles only, namely the two runs of thecompleted bundle which is formed by joining together the two partialbundles.

Known are also other methods of producing bundles of hollow fibers, forexample from the German publication DE-OS No. 3,102,331, in which thehollow fibers which are reeled on a spool are formed in an annular bodyof hollow fibers which is subsequently cut into individual bundles. Thedisadvantage of this known method is the fact that the entire mass ofthe spool and of the hollow fibers wound thereon must be constantly heldin rotation. For this reason, this method is also unsuitable for makingbundles of hollow fibers of freshly spun or extruded material.Accordingly, this prior-art method necessitates the use of fibers whichare already reeled on a spool. The cutting of the annular body of hollowfibers into individual bundles can be made also only during aninterruption of the winding operation, that means during the stopping ofthe spool.

It is true that there is known a large variety of methods and devicesfor producing bundles of hollow fibers of the aforedescribed kind, butsurprisingly all these prior-art methods are suitable for using hollowfibers which are already reeled on spools, thus necessitating aninterruption of the winding process when the wrapped-around strand hasattained a desired thickness, and this interruption in the prior-artmethods is unavoidable.

SUMMARY OF THE INVENTION

It is therefore a general object of the present invention to overcomethe aforementioned disadvantages.

More particularly, it is an object of the invention to provide animproved method which permits a rational production of bundles of hollowfibers in such a way that the preliminary winding of the fiber on aspool, which hitherto has been necessary, is no longer needed.

Another object of this invention is to provide such an improved methodwhich enables the production of bundles of freshly spun or extrudedhollow fibers.

A further object of this invention is to provide such an improvedmethod, in which the cutting of the wound-up hollow fibers intoindividual bundles and further processing of these bundles, for examplethe packing of the latter, can be performed on all bundlessimultaneously.

Still another object of this invention is to produce loose bundles ofhollow fibers which have a high heat-transfer or material-transfercapacity, that means for example which ensure a high throughflow rate orhigh clearance data.

Still another object of this invention is to provide such an improvedmethod which is generally applicable and can be easily adjusted toparticular operational conditions and individual requirements.

An additional object of this invention is to provide a method whichpermits a simultaneous production of bundles of hollow fibers havingdifferent lengths as well as the production of bundles of freshly spunor extruded, crimped or waved hollow fibers.

In keeping with these objects and others which will become apparenthereafter, one feature of the invention resides, in a method ofproducing bundles of hollow fibers by means of a movable guiding devicefor a continuous hollow fiber cooperating with at least two mutuallyspaced take-up elements arranged in the range of movement of the guidingdevice for taking up a strand of hollow fibers thereon. According to thenovel method, after reaching a desired thickness of the strand, that is,in cycles, the two take-up members together with the strand aredischarged from the winding position in the range of movement of theguiding device, and simultaneously another pair of empty take-up membersis fed into the winding position in the range of movement of the device,whereby if desired additional pairs of empty take-up elements arecyclically moved in the place of the preceding empty take-up elementsand then the strand on the first-mentioned take-up elements is cut intobundles of desired length.

The method of this invention is suitable for processing hollow fiberswound on a spool, as well as the freshly spun or extruded hollow fibers.Of course, the advantage of this invention takes effect in processingthe freshly spun hollow fibers. Under the term "freshly spun hollowfibers" are those produced in a wet spinning process, in a moldingspinning process, in a dry spinning process, or in other knownmanufacturing processes, whereby the wrapping of the hollow fibers intoa strand occurs generally in the condition in which, in prior-artmethods, the hollow fibers have been reeled on a spool. That is,conventional processing steps in liquid or gaseous media, cooling,drying, heat treatment and the like are performed before the creation ofthe strand, or if it is considered as advantageous these steps can bemade also at a later time point. It is also possible to process suchfreshly spun hollow fibers together with the previously reeled hollowfibers, combined at an arbitrary ratio, so as to form bundles of hollowfibers according to this invention.

As mentioned above, the production of bundles according to thisinvention is continuous, inasmuch as even a momentary interruption ofthe winding process results in considerable operational interferencesand in a high waste. After reaching the desired thickness of the strand,it is therefore necessary to remove the strand as fast as possible andwithout interference from the winding range. Depending on thearrangement of the fiber take-up elements, it is possible to withdrawthe completed strand from the take-up elements by hand. In practicehowever, such manipulation is in general unsuitable, inasmuch as thehollow fiber bundles can become dirty or damaged. Moreover, theprocessing of the strands of hollow fibers in bundles, namely thecutting of the strand into sections and the subsequent packing and thelike, can be performed generally only at a certain tension of the hollowfibers. For this reason, the strand of hollow fibers should maintain itsinitial shape as long as possible. Accordingly, it has been proved to beof particular advantage when, in the production method of thisinvention, the strand of hollow fibers, after reaching the desiredthickness, is withdrawn together with the supporting take-up elementsfrom the winding range of the guiding device, and simultaneously anempty set of fiber take-up elements is fed into the winding range andplaced into the correct winding position.

This procedure permits an uninterrupted processing of freshly spunhollow fibers in strands for arbitrarily long time periods.

In the method of this invention it is possible to process a singlecontinuous hollow fiber, or if desired it is also possible to processsimultaneously a large number of such continuous fibers, for exampletwenty or more, which are wrapped as a cable around the take-up elementsto form the strand. In wrapping the fiber around two spaced take-upelements, a strand is formed having an elongated O-shaped configuration.In wrapping or winding the hollow fiber around more than two take-upelements which are not in alignment with one another, a strand willresult having the form of a polygon. During the formation of the strandof hollow fibers, the wound-up fibers remain in rest in the range ofmovement of the fiber guiding device. Only after reaching the desiredstrand thickness, that is when the strand contains as many windings asthere are hollow fibers required in the completed bundle, is the stranddischarged from the winding range swept over by the guiding device, andthe set of empty take-up elements is conveyed in the winding range sothat the guiding device starts wrapping the fiber around newly suppliedset. Hence, the withdrawal of the wound-up hollow fibers in the methodof this invention is not continuous, but is made cyclically. Thisfeature has the great advantage that during the standstill of thecompleted strand of the hollow fibers, that is during the time periodbetween the momentary motion cycles, all conventional processing stepscan be performed on the stationary strands, such as ror example,binding, cutting into bundles of desired lengths, packing, and the like.

In producing a polygonal strand of hollow fibers in which each side ofthe polygon corresponds approximately to the length of the bundles to beproduced, it is possible to simultaneously produce a bundle of hollowfibers from respective sections of the polygonal strand.

The method of this invention makes it possible also to producesimultaneously bundles of hollow fibers having different lengths. Forthis purpose, there are employed at least three fiber take-up elementsarranged in a polygonal configuration and wrapped by the hollow fiber insuch a manner that a polygonal strand having sides of different lengthsis created, whereby the lengths of the sides correspond approximately tothe lengths of the produced bundles. In a modification, the sides of thepolygon can have the same length, so that bundles of hollow fibershaving different lengths in different proportions can be produced fromthe strand. There is also the possibility to unite several bundles ofhollow fibers of the same length into a single, more voluminous bundle,or to produce in this manner bundles having different numbers of hollowfibers.

The method of this invention is suitable for processing all kinds ofhollow fibers in bundles of arbitrary thickness. Accordingly, it ispossible to produce bundles which are suitable for exchange ofsubstances or the transfer of substances, for heat transfer, for thecombined substance-heat transfer, or for other conventional applicationsof hollow fiber bundles.

Freshly spun hollow fibers in general have a smooth upper surface andusually are obtained in a substantially straight, only slightly bentshape. This shape is desirable for many applications and has itsadvantages. However, this shape of hollow fibers has frequently theconsequence that, when the fibers are united in a bundle in whichcontact between the fibers is established over long linear stretches, apart of the adjoining upper surface which affects the heat- or materialexchange, becomes ineffective. Also, a uniform circulation of a mediumaround all hollow fibers assembled in a bundle is frequentlyunwarranted. In such instances. it is advantageous to process hollowfibers which are to be assembled with a random orientation in a bundlewithout the use of spacers, in such a manner as to impart to the fibersa form which is considerably different from the rectilinear form. Suchdeformed hollow fibers facilitate the creation of loose bundles whichexhibit an increased quality of the heat- or material transfer throughthe hollow fiber bundle.

Devices for curling or crimping hollow fibers have already been devised.Hollow fibers which have been crimped in accordance with known methods,however, are designed for a subsequent processing into rayon or staplefibers, for use as filling material in cushions, clothing, and the like.For this reason, in prior-art crimping processes it was not consideredas a disadvantage when the fibers became cracked or heavily damaged. Onthe contrary, in such methods it was intentionally aimed to split thehollow fibers during the crimping, or to divide the fibers intoindividual fibriles. Therefore, such known methods are not suitable forshaping hollow fibers in a form deviating from a rectilinear formwithout making the resulting fibers unusable for the aforementionedapplications.

Shaping of the hollow fibers in a form which improves the transferquality of hollow fiber bundles, and in which the probability of damageof the processed fibers is reduced almost to zero, is achieved accordingto another feature of this invention when the hollow fibers areundulated. A hollow fiber waved in accordance with this invention has,in the preferred embodiment, the form of a uniform sinusoid lying in oneplane, or a zig-zag undulation in one plane with alternating bent andunbent sections, whereby the bent sections in which the fiber changesits direction exhibit no cracks or buckles but have a sufficientlydimensioned radius of curvature. In a modification, the fibers undulatedaccording to this invention have the form of a helical spring (a curl)which upon stretching of the fiber transits into a flat waveform. Thewaveform of the fibers resulting by the method of this invention doesnot include the shape resulting when a non-undulated hollow fiber in theform of a polygon, resulting for example by winding around acorresponding spool and subject in this form to a fixation process. Inthe latter form of undulation, no change in direction takes place at thesite of bending in the manner as achieved by waving the fiber accordingto this invention. Moreover, the amplitude of the waves is too small,and the length of the waves is excessively large, and consequently incomparison with results obtained by the wavy shape of this inventionwith regard to the transfer capacity of the hollow fiber bundles cannotbe achieved. The undulation of hollow fibers according to this inventioncan be irregular, but nevertheless with a certain periodicity, that iswith a regular repetition of the same irregular pattern. In practicehowever, it has been found that a regular waveform of the hollow fibers,such as a regular sinusoid or a zig-zag pattern or a regular helicalpattern, is more advantageous.

The processing of strands of undulated hollow fibers into bundles ispreferably made in a quasi-stretched condition of the fibers. Theloosening of the bundle of hollow fibers can be made for example duringits installation in a housing, thereby the installation space in thehousing has a length which is shorter than the length of the fibers inthe bundle in the stretched condition.

The undulation or waving of freshly spun hollow fibers must be made alsoin such a manner that the continuity of the production of hollow fibersis not impaired or even interrupted. This means that the undulation orwaving is performed either continuously before the winding of the fibersin the strand on the take-up elements or, alternatively, the waving isperformed after a completed strand is withdrawn from the winding area.In the latter case, the undulation of hollow fibers is made only afterthe cutting of the strand into the bundles.

In order to produce waving of tne hollow fibers, the latter are broughtpreferably in a predetermined recurrent form and subject to a fixingprocess in this form, so that at the end of the treatment the fiberspreserve at least partially the shape of this form. In searching for asuitable fixation method, it should be taken into consideration what isthe intended use of the hollow fiber bundles, so as to preclude that thewavy shape imparted to the fibers be not lost during the operationalapplication of the bundles.

Depending on the type of processed hollow fibers, a longer time intervalmay be needed for fixing the wavy shape. For example, the passing ofhollow fibers through a gap between teeth of two gears which rotate inmesh with one another without contact would not be sufficient forimparting a permanent undulation to the fibers, because the processingtime and speed would be reduced to an intolerable level or, from thetechnological point of view, can be realized only with greatdifficulties. According to this invention, a method is devised in whichthe hollow fibers are guided in a zig-zag fashion about round rodsarranged in two planes, and being spaced one from the other so as toundulate the hollow fiber with tne same speed at which the fibers arepassed through the fixing zone. A device which makes this methodpossible will be described below in connection with the Figures.

In carrying out this novel method, the distance between the fibertake-up elements and the wavelength of the undulation of the hollowfibers are dimensioned such that in the completed bundle of hollowfibers the undulations are arranged relative to each other with a phaseshift. that is the valleys and the crests of the undulations ofadjoining fibers are located at different points. This phase shift canbe achieved also in a different manner, for example so that theindividual fibers in a strand are subject in the fixing zone toundulations at different wavelengths or, alternatively, in the case ofuniform wavelengths they are shifted relative to each other in thefixing zone. Such a phase shift of the waved hollow fibers can beachieved also by providing for the hollow fibers different stretchesbetween the waving zone and the strand wrapping device, for instance byadjusting different deflections of the fibers.

Provided that the hollow fibers have a sufficient strength, they can bealso drawn about a stationary round rod having a thread-like groove, andin doing so the fibers can be simultaneously subjected to a fixingprocess so that the helical form which is imparted to the fiber on thescrew-like rod is fixed.

Preferably, according to the method of this invention the undulatedhollow fibers are discharged from the waving zone substantially in astretched condition, and then wound in the strand.

In the case when the waving of the hollow fibers is to be made after theformation of the strand, then it is recommended that the strand be firstdivided into hollow fiber bundles of the desired length and thereforethe bundles are subject to undulation in the desired waveform, andsubsequently this waveform is fixed in a fixing provision.

The undulation or waving can be also carried out in discrete sections,so that undulated sections in a completed bundle alternate withnon-undulated sections.

By simple tests it is possible to find out whether it is necessary towave all hollow fibers in the bundles, or whether it is sufficient whenonly a part of the fibers is undulated and what is the minimumproportion between the undulated and straight hollow fibers in eachbundle.

Hollow fibers which in order to preserve their form at least duringtheir manufacture are filled with a liquid or a pressurized gas are ofcourse less susceptible to folding in their bending or deviation points,so that in this case smaller radii of curvature can be selected than inhollow fibers which are being processed without the use of pressurizedliquid filling up their volume. Different limit measures for the radiiof curvatures at which the folding of hollow fibers is avoided aredetermined in dependence on the mode of processing of the hollow fibers,namely whether they are undulated before their wrapping on the take-upelements or only after the cutting of the strand when the fluidcontained in the hollow fibers has the opportunity to escape from thelatter.

As mentioned before, in the method of this invention both the strand ofhollow fibers which is being wound in the processing zone, and thecompleted strand or strands which were discharged from the winding zone,remain mostly in a stationary condition which is interrupted onlyintermittently by momentary transportation steps in the manner which hasbeen explained before. Provided that the wrapping or winding of thehollow fibers on the take-up elements is performed in such a way thatthe completed strand of hollow fibers lies in a substantially horizontalplane, then all straight sections of the strand which are used for theproduction of hollow fiber bundles are located at the same level even inthe case of polygonal strands. Due to this feature the subsequentprocessing of the strand in bundles is substantially facilitated,inasmuch as it is possible that several workers can simultaneouslyoperate at different sides of the strand. Substantially greateradvantages are offered by this kind of strand production when it isaimed to automate as many processing steps as possible, such as forexample the compounding of the aforementioned sections of the strand,the cutting of the same into bundles, or packing the same. Moreover, bythis means it is possible to perform all these processing stepssimultaneously at all sections of the strand by providing devices at thecorresponding sections which will be described in greater detail belowand are illustrated in the Figures. The automation results in shorteroperational cycles both for completion and discharge of a strand offibers and the subsequent operational steps are made in correspondinglyshorter time intervals.

The method of this invention has proved to be of particularly advantagein manufacturing bundles composed of extremely sensitive and thin-walledhollow fibers which necessitate a delicate processing and treatment, andwhich are prone to damage, breakage, and the like undesiredcontingencies during their manufacturing and processing. For example, byusing the method of this invention, it is possible to successfullyhandle without increasing normal percentage of waste the freshly spunhollow fibers produced by regeneration of cellulose fromcuprammonium-cellulose solutions, in hollow fiber bundles of theaforedescribed kind, which can find application for example incommercially available dialyzers, whereby excellent urea-clearancevalues are obtained. Such hollow fibers, after extrusion from thespinning nozzle, pass through different washing and treatment stationsin which the fibers are immersed in various liquid baths and driedbefore their winding. During this processing cycle the waving of thehollow fibers can be made for example in the drying zone, whereby thestill wet hollow fibers are shaped with the desired waveform and thendried in conventional manner in bulk before, by applying a slight butsufficient tension to the fibers, they are again stretched in a linearform and wound in a strand on the take-up elements.

The method of this invention is successful in the production of bundlesof hollow fibers whose wall thickness is in the range between 3 and 20microns, and whose inner diameter is in the range between 100 and 300microns. Preferably, the processed hollow fibers have a wall thicknessof about 5 microns or 8 microns and an inner diameter of about 150microns or approximately 200 microns.

Hollow fiber bundles made of freshly spun fibers and waved according tothis invention have typically a urea-clearance which is 75-100% higherin comparison with bundles made of non-undulated fibers.

Hence, the method of this invention permits for the first timeproduction of bundles of hollow fibers having the requisite material-and heat transfer quality without necessitating the hitherto unavoidablestage of reeling the hollow fibers on spools serving as the startingstage in the production of the bundles. The possibility to process inbundles the hollow fibers in their original condition as well as inwaved condition with an arbitrary intensity of waving, means that themethod of this invention is practically unlimited with regard to itsadjustment to the needs and operational requirements of the finalproduct, and is capable of further modifications and developments on thebasis of the inventive concept.

The increase of the heat- and material transfer quality of bundles ofundulated hollow fibers with respect to bundles composed ofnon-undulated fibers can be determined at least qualitatively bymeasuring pressure losses of a fluid passing through the hollow fiberbundles. For this purpose a bundle of undulated hollow fibers producedaccording to this invention is accommodated in a correspondinglydimensioned, preferably tubular housing, which at the ends of the bundleis connected to pressure-measuring devices. When a fluid such as waterflows through the hollow fiber bundles, then the pressure loss which isdependent on the time rate of the stream volume can be determined. Whenin the same or similar housing a bundle of non-undulated hollow fibersis inserted and is the same measurement is performed, then it will berecognized that the bundle of undulated hollow fibers produces a higherpressure loss than a bundle of non-undulated fibers. To make thisdifference more apparent, it is recommended to employ a bundle assembledof very long fibers for performing such measurements. Besides, thehollow fibers can be closed at one end, so that no throughflow occurs,but the medium circulates around the fibers. In this manner, only thepressure loss produced by the flow of the medium around the hcllowfibers in their longitudinal direction becomes effective.

Comparative measurements were made by way of an example on a bundle offreshly spun non-undulated hollow fibers acquired by regeneration ofcellulose from a cuprammonium-cellulose solution, and of correspondinglyproduced undulated fibers. The length of the bundles amounted to 250 mm,and the bundle contained 1000 hollow fibers having an outer diameter ofabout 216 microns and an inner diameter of about 200 microns, andaccordingly a wall thickness of about 8 microns, when measured in driedcondition. Each bundle of hollow fibers was arranged in a pipe of aninner diameter of 14 mm. The ends of the fibers were closed, so thatonly pressure loss resulting from the circulation of the medium aroundthe fibers was measured. The hollow fibers in the second bundle had azig-zag waveform with a wavelength of about 20 mm and an amplitude ofabout 1 mm.

A stream of water at a temperature of 37° C. circulated in longitudinaldirection of the fibers around the bundle. The rate of flow was 2.4liters per hour. Under these conditions the pressure loss in the case ofthe bundle of non-undulated hollow fibers was about 4 mm Hg, whereas inthe bundle of undulated hollow fibers the pressure loss was about 26 mmHg. The urea-clearance for the bundle of non-undulated hollow fibersamounted to 95 ml per minute, whereas in the bundle of undulated hollowfibers the clearance was 163 ml/min. Inasmuch as the clearance in thebundle of undulated hollow fibers did not increase in the same extent asdid the pressure loss, when compared with the bundle of non-undulatedhollow fibers, the experiment shows clearly that the bundle of undulatedhollow fibers produced according to this invention, exhibits a higherpressure loss as well as a substantially higher urea clearance than abundle of non-undulated hollow fibers according to this invention.

In the following paragraphs, a general description of most importantfeatures of a device and its embodiments will be presented.

The device for producing a strand of hollow fibers has the followingcharacteristic features: A movable fiber guiding member, at least fourfiber take-up elements arranged in pairs and being supported formovement in such a manner that at least a pair of fiber take-up elementsis forced to stay in a preparatory position outside the winding rangeswept over by the fiber guiding device so long until another pair oftake-up elements is present in a working position in the winding range,whereby the first-mentioned pair of take-up elements is displaced fromits preparatory position into the working position in the winding rangewithout impairing or interrupting the winding process by the guidingmember, while the first-mentioned pair of take-up elements is dischargedfrom the winding range.

In an embodiment of the device of this invention, there can be providedan arbitrary number of groups of fiber take-up elements, each groupcontaining either the same number or a different number of theseelements. In order to cut the hollow fiber strands into individualbundles, and to bind or pack the bundles, there can be providedadditional devices for performing these functions.

The fiber guiding device or member can move either along a circular pathor along a longitudinal closed path such as for example an ellipticalpath, or can move back and forth along a rectilinear path or along acircular section. When the fiber guiding member performs a reciprocatingmovement, the pair of fiber take-up elements located in the workingposition below the guiding member moves back and forth in the directionwhich is substantially perpendicular to the direction of movement of theguiding member. This back and forth movement of the take-up elements isperformed always at the point when the fiber guiding member reaches itsend position, whereby the take-up elements cross the path of the guidingmember.

The device for producing bundles of undulated hollow fibers exhibitsadditionally the following characteristic features: a device by means ofwhich the hollow fibers are forcibly shaped in a sinusoidal shape,in azig-zag, and the like. This undulating device can be arranged before thestrand forming device and be moved with the same speed at which thehollow fibers are fed to the winding device; there is also provided afixing zone in which the wavy shape imparted to the hollow fibers ispermanently fixed.

The novel features which are considered characteristic for the inventionare set forth in particular in the appended claims. The inventionitself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic side view of a first embodiment of the device ofthis invention for producing strands of hollow fibers by means of twopairs of fiber take-up elements;

FIG. 2 is a top view of the device of FIG. 1;

FIG. 3 is a modification of the device of FIG. 1 including four pairs offiber take-up elements;

FIG. 4 is a side view of still another modification of the device ofFIG. 1, including three pairs of fiber take-up elements;

FIG. 5 is a front view of the device of FIG. 4;

FIG. 6 is a top view of the device of FIG. 4;

FIG. 7 is another embodiment of the device for producing strands ofhollow fibers, including two groups of fiber take-up elements arrangedin regular hexagons each including six elements;

FIGS. 8a-8d show schematically possible modifications of the device ofFIG. 7 for producing different polygonal shapes of different size of theproduced hollow fiber strands;

FIG. 9 is a side view of another embodiment of the device of thisinvention for producing strands of hollow fibers by means of a pluralityof pairs of fiber take-up elements arranged on an endless band or chainconveyor and cooperating with a fiber guiding device moving along anelongated closed path;

FIG. 10 is a top view of the device of FIG. 9;

FIG. 11 is a modification of the device of FIG. 9, in which the fibersguiding member moves back and forth along a rectilinear path;

FIG. 12 is a front view of the device of FIG. 11;

FIG. 13 is a top view of an embodiment of the device of this inventionfor producing strands of hollow fibers by means of a pair of fibertake-up elements cooperating with a fiber guiding member which ismovable back and forth along a curved path;

FIG. 14 shows in a sectional side view a device for facilitating thetransfer of completed hollow fiber strands;

FIG. 15 is a side view of a device for continuous undulation of one ormore hollow fibers used in bundles produced according to this invention;

FIG. 16 is a side view of a cut away part of the device of FIG. 15,shown on an enlarged scale;

FIG. 17 is a sectional front view of the device of FIG. 16, taken alongthe line XVII--XVII;

FIG. 18 is a side view of another embodiment of a cut away part of adevice for imparting intensive waving to hollow fibers;

FIG. 19 is a sectional front view of the device of FIG. 18;

FIGS. 20-26 illustrate in sectional side views various arrangements ofrod-like members of the devices of FIGS. 15-19 for imparting a desiredwave shape to the fibers;

FIG. 27 shows in a front view a device for continuous waving of one ormore hollow fibers, whereby the resulting undulated fiber has the formof a helical spring;

FIG. 28 is a side view of the device of FIG. 27;

FIG. 29 is a device for adjusting the deflection of undulated hollowfibers so as to produce a phase shift between individual fibers arrangedin a strand or bundle;

FIG. 30 shows a side view, partly in section, of a device for continuousundulation or waving of hollow fibers, the device having the form of athreaded rod, of which the fiber is forcibly guided so as to receive ascrew-like wave shape;

FIG. 31 shows a modification of a device for undulating bundles ofhollow fibers produced according to this invention, whereby the bundleis wound up on a round rod and in this condition undergoes a fixingprocess;

FIG. 32 is another modification of a device for undulating hollow fibersby means of a tubular body in which a helically shaped fiber is insertedand subject to a fixing treatment;

FIG. 33 shows in a top view a preferred embodiment of a device forproducing strands of hollow fibers in the form of a regular hexagonarranged in one plane;

FIG. 34 is a side view partly in section of the device of FIG. 33;

FIG. 35 is a side view of a device for packing hollow fiber bundlesproduced according to this invention;

FIG. 36 is the device of FIG. 35, shown in its packing position;

FIGS. 37-40 illustrate different wave shapes of hollow fibers in thebundles produced according to this invention; and

FIGS. 41 and 42 show in side views different modifications of the fiberguiding members.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 illustrate an embodiment of a device for producing strandsof hollow fibers. The device includes a fiber guiding member 1, a firstpair of fiber take-up elements 2a, a second pair of fiber take-upelements 2b, both pairs of take-up elements being fixedly mounted on anendless conveyor belt 4 circulating about two conveyor rolls 5 and 6.The rollers keep the conveyor belt in taut condition and are set intorotation by non-illustrated driving means. A rotary fiber guiding member1 is arranged above the upper run of the conveyor belt and rotates aboutan axis of rotation in the direction indicated by an arrow. The upperend of the guiding member 1 coincides with the axis of rotation, whereasits lower end is offset from the latter, so that hollow fiber 3, whichis fed in the guiding device in the direction of its axis of rotation,is guided at the outlet end along a circular path enclosing a workingposition of the first pair of take-up elements 2a, so that the hollowfiber 3 is wrapped around the two take-up elements, and an elongatedstrand 35 is wound on the latter. After a sufficient length of thehollow fiber has been wound on the take-up element 2a and the desiredthickness of the strand 35 has been reached, the drive of the conveyorbelt is activated, the first pair of take-up elements 2a together withthe wound-up hollow fiber strand are moved out of the range of windingto the left, and simultaneously the empty pair of take-up elements 2badvances to the vacant working position in the winding range of theguiding member 1, which continues its winding operation. At this moment,the advance of conveyor belt 4 is stopped, and a new strand is wrappedaround the elements 2b. The completed hollow fiber strand, which is nowlocated in a non-illustrated processing position at the left end of theconveyor belt, can be removed from the take-up elements 2a or be cutinto bundles of hollow fibers of desired length, while the second strandis being formed on the take-up elements 2b. After the second strand iscompleted, the conveyor belt is activated to move to the right so thatthe first pair of take-up elements 2a is again in the working positionin the winding range of the guiding member 1, and the hollow fiber 3without interruption is again wound around the first pair of elements2a. The above described operational steps can be repeated with anarbitrary frequency.

In the embodiments of the device of this invention illustrated in FIG.3, there are provided on the conveyor belt 4 eight take-up elements 2arranged in four pairs. In this embodiment, the conveyor belt 4 isintermittently activated in the same direction indicated by dashedarrows. The momentary advance of the conveyor belt lasts so long until apair of empty take-up elements is situated in the working position inthe winding range of the guiding member 1.

A modification of the device of FIG. 3 is illustrated in FIGS. 4-6, inwhich three pairs of take-up elements 2 are arranged on the conveyorbelt 4, which also intermittently circulates in the same directionindicated by the dashed arrow. In this embodiment, the conveyor belt isadjusted vertically so that the conveyor roller 5 is located in thewinding range of the member, and the other conveyor roller 6 is locatedbelow the roller 5. The six take-up elements 2, which are arranged inthree pairs, are hook-shaped so as to prevent the slippage of thecompleted hollow fiber strand 35 when the conveyor belt is activated andthe strand is displaced into its processing position.

The hollow fiber strands produced in the devices according to FIGS. 1-6have a stretched O-shape. Even this form can be considered as apolygonal form, defining two angles.

In the embodiment of the device for producing hollow fiber strands 35according to FIG. 7, there are provided two groups of six fiber take-upelements 2a and 2b mounted on the conveyor belt 4 and each forming arectangular hexagon. The remaining component parts of the device, suchas rotary fiber guiding member 1 and the driving rollers 5 and 6, areidentical with those in the preceding embodiments and are notillustrated. By wrapping one or more hollow fibers 3 around the take-upelements 2a or 2b a strand 35 is formed which has the form of a regularhexagon. By cutting the straight parts of respective sides of thehexagon, that is those parts which extend between the curved portions ofthe fibers adjoining the round take-up elements, altogether six bundles33 of the same length are produced. This length is only slightly shorterthan the center distance of two opposite take-up elements 2a or 2b.Otherwise, the mode of operation of this embodiment corresponds to thatof the devices of FIGS. 1 and 2.

By changing the number of take-up elements in respective groups 2a and2b in the device of FIG. 7 and wrapping the hollow fiber or fibersaround the remaining take-up elements, it is possible to obtain hollowfiber strands of different polygonal configurations, as illustrated inexamples of FIGS. 8a-8d. FIG. 8a shows a strand in the form of anequilateral triangle, FIG. 8b the strand in the form of a rectangle,FIG. 8c a strand having the shape of a triangle with three unequallengths of its sides, or in FIG. 8d an irregular quadrilateral whoseadjoining sides have the same length. In this manner it is possible toproduce simultaneously hollow fiber bundles of different lengths. If thenumber of take-up elements 2a and 2b in each group is increased from sixto twelve, for example, so as to form a regular dodecagon, then byremoving one or more take-up elements a substantial increase ofvariation possibilities will result in order to produce hollow fiberbundles of different lengths. In addition, the fiber take-up elements inrespective groups can be arranged in different polygons processed oneafter the other.

The operation of devices according to FIGS. 9 and 10 for producinghollow fiber strands is basically the same as in the preceding examples,except in the arrangement of the fiber guiding device 1 which does notrotate about an axis of rotation but orbits along an elongated closedpath 7. The path 7 can be also elliptical.

In FIGS. 11 and 12, there is illustrated a device for producing hollowfiber strands in which the fiber guiding member 1 is arranged for areciprocating movement along a rectilinear path 8. For this purpose, thefiber take-up members 2, at least in their working position, must beswingably supported in such a manner that after the fiber guiding member1 reaches an end point of its path of movement, the pair of take-upelements 2 is displaced in transverse direction to its opposite endposition. In this manner it is made possible that the hollow fiber iswrapped around the spaced take-up elements 2 even during the rectilinearmovement of the guiding member. Hence, this path is always crossed bythe reciprocating take-up elements. The back and forth movement of thetwo take-up elements 2 can be imparted by means of a pneumatic,hydraulic or magnetic actuator 36, by a crank drive, or the like. Onlyduring the intermittent motion of the conveyor the oscillating drivemust be temporarily disengaged from the take-up elements 2. In FIG. 11there is illustrated a control device 37 including axially mounted rollswhich act as an energy store to compensate for variations in the tensionof the hollow fiber supplied to the guiding member or discharged fromthe latter, thus guaranteeing a constant tension of the wound aroundfiber. These fiber oscillations are neutralized by the upward anddownward movements of the suspended roll 37a. This tightness-controllingdevice 37 can be also arranged in a regulating circuit which affects therotary speed of the fiber guiding device 1 in such a manner as tosynchronize the intake velocity of the fiber with its discharge.Moreover, the tightness control device 37 of this type or of anothertype performing the same function can be also provided in the previouslydescribed embodiments of the device of this invention. Thetightness-controlling devices influence in favorable manner theinterference-free exchange of the wrapped up and empty take-up elements2 during their cyclic advance.

Instead of moving back and forth on a rectilinear path, the fiberguiding member 1 can perform a reciprocating movement on a curved path8a, as illustrated in FIG. 13. The corresponding back and forth movementof the fiber take-up elements 2 in their working position is performedin the same manner as described before in connection with FIGS. 11 and12.

FIG. 14 illustrates equipment which substantially facilitates thelifting of a non-illustrated hollow fiber strand from the take-upelements 2. This equipment includes tubular attachments 9 closed attheir upper ends and insertable on the take-up elements 2. Theattachments 9 are interconnected by rod- or plate-like spacer 10 whichsupports the completed strand during its transportation, so that thelatter does not change in its form. Similar aid can be used also forarrangements including more than two take-up elements 2. For example,hollow fiber strands of hexagonal configuration can be transported on acorresponding arrangement of the attachments 9 and the spacer 10.

Instead of conveyors employing bands 4, chains and the like asillustrated in FIGS. 1-14, the fiber take-up elements 2 can be arrangedin pairs or larger groups also on an annular disk which is rotatableabout its center axis and cyclically activated (carousel principle).Another modification which is technologically more expensive, thetake-up elements are fixed on a stationary plate, and the entire windingdevice, that is the fiber guiding member together with its drive andother component parts, is cyclically moved from one group of take-upelements to the next one. In the embodiment using a rotary support forthe take-up elements 2, all pairs or larger groups of these elementshave the same distance from the rotary axis of the supporting plate. Incontrast, in the embodiment using the movable arrangement of thecomplete winding device, the arrangement of the groups of take-upelements can be arbitrary. In a further elaboration of this invention,the positioning of the pairs or larger groups of take-up elements can becontrolled according to a program. Furthermore, the conveying means forthe take-up elements 2 can be arranged in a single plane and can becyclically moved similarly as conveying bands used in airports fordischarging baggage.

FIG. 15 illustrates, in a schematic form, a device for continuouslyundulating hollow fibers prior to their processing into bundles. Thedevice includes a pair of superimposed roller chain loops 11 and 14circulating in opposite directions as indicated by arrows. Each of theroller chain loops carries a plurality of uniformly distributed,horizontally oriented rods 12 and 14 of circular cross section. Theround rods 12 in the upper chain loop 11 are spaced apart by the samedistance as the round rods 14 on the lower chain loop 13. It will beseen from FIGS. 15-17 that the rods in the lower run of the upper chainloop 11 interleave with the rods in the upper run of the lower chainloop 13, so that hollow fiber 3, which is acted upon by the interleavedround rods, is shaped into a wavy or zig-zag form which can be fixed ina fixing zone 34. For the sake of clarity, driving rollers for the chainloops 11 and 13, as well as other conventional equipment such as chainguides, chain deflecting and tensioning wheels, and the like, areomitted in the Figure. It will be noted that if only a slight undulationor waving is desired there can be employed two endless toothed belts orconveyor belts provided with a similar toothing, whereby the teeth ofthe facing runs are in mesh without actually engaging each other.

FIGS. 16 and 17 show in greater detail on an enlarged scale variousviews of a cut away part on the device of FIG. 15. The duration of theexposure of the fiber 3 to the undulating rods 12 and 14, or to themeshing teeth of the gears, can be adjusted by the correspondingdimensioning of the length of the roller chain loops 11 and 13 or by therotary speed of the gears. Also, the bending radius of the fibers 3about the round rods 12 and 14 is controlled by the selection of asuitable radius of these rods. Of course, instead of roller chain loops11 and 13, it is possible also to employ other types of endless bands,belts and the like. Also, the unilateral fastening of the round rods 12or 14 as illustrated in FIG. 17 can be replaced by the arrangement inwhich two parallel chain loops support the shaping rods at both endsthereof.

Such a double-sided support of the round rods 12 and 14 is illustratedin FIGS. 18 and 19. In this embodiment, the clearance between the roundrods 12 and 14 in the straight section of the runs of the chain loops 11and 13 is less than the maximum depth of engagement. As a consequence,this arrangement permits a particularly intensive waving of the hollowfiber 3, inasmuch as the looping produced by the interleaved round rods12 and 14 is increased and the hollow fiber 3 therefore is bent overlonger sections of the fiber. As in the preceding example, the bentsections of the fibers are fixed in a fixing zone 34. In this manner,the waveform produced by the device of FIGS. 18 and 19 has a largeramplitude, and consequently after stretching the waved hollow fiber 3 alarger wavelength is obtained.

The embodiments of FIGS. 15-19 show how to adjust the waving intensity,that is the amplitude or the wavelength of the hollow fibers 3 undulatedaccording to this invention.

FIGS. 20-24 show different configurations of undulating elementscorresponding in function to round rods 12 and 14 in FIGS. 15, 16 and18. The rods are provided with a central groove of different crosssection which ensure a better guiding or engaging of the hollow fiber 3supplied individually or as cables or in bands during their waving inthe fixing zone 34. The diameter of the undulating rods 12-14 can be forexample between 15 to 20 times larger than the diameter of the hollowfibers, provided that no folding or splitting of the fibers in bendingareas will occur. For example, hollow fibers of regenerated cellulosehaving a diameter between 150 and 200 microns can be undulated by meansof round rods of 3 mm diameter with a depth of engagement between 0 and5 mm and at a center distance of the rods of about 9.5 mm, withoutfolding or splitting.

In the arrangement of the fiber waving device illustrated in FIGS. 25and 26, the hollow fiber or fibers 3 are guided substantially in anintermediate plane between two parallel chain conveyors, each supportinga plurality of round rods inclined at an acute angle to the intermediateplane. It will be seen from FIG. 26 that the hollow fiber is undulatedto a depth which corresponds to the diameter of the round rods.Accordingly, the waving achieved in this arrangement has only a smallamplitude, which, however, may be of advantage in many applications.

By an irregular distribution or by leaving gaps in a regular arrangementof the round rods 12 and 14, a corresponding irregular undulation isimparted to hollow fibers 3, so that alternating successions ofundulated and straight fiber sections are produced. The round rods 12and 14 can be also arranged in such a manner as to produce alternatelydifferent depths or amplitudes of the waving. For example, by combiningthe embodiments according to FIGS. 15-17 with FIGS. 18 and 19, differentwaving amplitudes can be obtained. If a shrinkage occurs during theundulation of the hollow fiber 3, then in order to prevent breakage orstretching stress in the latter, an arrangement can be selected in whichthe depth of engagement of interleaving round rods 12 and 14 graduallydecreases in the feeding direction of the fiber in accordance with theshrinkage. In the production of hollow fiber bundles according to thisinvention, it is possible to form the strand of hollow fibers ofundulated fibers and of a portion of straight hollow fibers so that amixture of undulated and non-undulated fibers is contained in the strand(FIG. 40).

FIGS. 27 and 28 illustrate an embodiment of a device for continuouswaving of hollow fibers 3. The device consists of a plurality of roundrods 15 which are supported for rotation about their longitudinal axesand are uniformly arranged in a circle. A continuous hollow fiber 3, ora cable of several hollow fibers, is wound around the rotary rods 15,and the resulting helical form is fixed. In this manner, the fibersobtain a corresponding wavy form. The withdrawal of the undulated hollowfibers from the crown of the freely rotatable or driven round rods 15occurs with a minimum lateral slippage, so that this arrangementprovides a particularly protective process of imparting undulation tothe fibers. Guiding rings 17 provide for fixed feeding and dischargingpoints at the waving run.

FIG. 29 illustrates means for achieving a phase shift of undulatedhollow fibers in a strand or bundle. For this purpose the hollow fibers3 are guided between round rods 18-20. The guiding rods 18 and 19 aresituated in the feeding direction of each fiber, whereas theintermediate guiding rods 19 are laterally offset from the feedingdirection. The deviation imparted by the intermediate guiding rods 19 isdifferent for each hollow fiber, so that different lengths 3a-3f aredeviated between the uniformly spaced guiding rods 18 and 20. It will beseen from FIG. 29 that the deviated section 3a in the uppermost hollowfiber is laterally offset to a substantially larger degree than thelowermost hollow fiber sections 3f. By suitably adjusting the clearancebetween the fiber guiding rods 18 and 20 and the position of theintermediate guiding rods 19, it will be achieved that the undulatedhollow fibers 3 in completed bundle are shifted in phase relative toeach other (FIG. 38).

In the embodiment of FIG. 31, the hollow fiber 33 is wound around asingle rod 21 and the resulting helical configuration is subject to afixing process. Hollow fibers of a material having a sufficient strengthcan be continuously undulated on the device illustrated in FIG. 30. Inthis arrangement, hollow fiber 3 is wound in screw-like grooves 23 of athreaded rod 22 and continuously drawn in one direction. The impartedhelical form is again fixed so that the fiber obtains a permanentundulation.

The embodiment of an undulating device according to FIG. 32 is suitableparticularly for undulating fibers 3 or fiber bundles 33 of a definitelength. The fibers 3 are rotated to obtain a helical form and are fedinto a tubular container 24 where they are subject to a fixingtreatment. The container 24 can be provided with a rigid or flexiblecentral core which facilitates production of a coil of the hollow fiberswith a desired density.

FIGS. 33 and 34 illustrate a particularly advantageous embodiment of adevice for producing strands of hollow fibers according to thisinvention. In this arrangement, the fiber take-up elements 2 have aU-shaped configuration and are arranged in pairs which are uniformlymounted on a plurality of roller chain conveyors 25. In this example,there are used altogether six chain conveyors 25 forming together ahexagon. The lower chains 25 are driven and held in taut condition bysprocket wheels 26 arranged one above the other. The fiber guidingdevice 1 includes a rotary guiding arm 27 which rotates along a circularpath circumscribing the six U-shaped take-up elements 2 located in thewinding position at the upper wheel 26. The hollow fiber is laid in theslot 28 between the arms of the take-up elements. After reaching thedesired thickness of the hexagonal strand, all six roller chains 25 aresimultaneously activated to displace the completed hollow fiber strand35 from the winding position to a processing position, while a new setof six empty take-up elements 2b in the working position in the windingrange of the arm 27. Thereafter, the roller chain conveyors 25 areswitched off, and during the standstill the completed strand isprocessed by cutting, packing, and the like, into the bundles.

Examples of a preferred embodiment of a device for processing thecompleted hollow fiber strand 35 into bundles 33 is illustrated in FIGS.35 and 36. This device, which performs the embracing, clamping andpacking of the bundle 33, is illustrated in its ready position on theright-hand side in FIG. 33. The device includes an endless band 30rotatable about five rollers 29, of which the upper rollers 29a aremovable in opposite directions as indicated by arrows in FIG. 35. In astarting position in which the rollers 29a are spaced apart from oneanother, a packing foil 31 or the like is laid on the belt sectionbetween the rollers 29a, and the whole device is moved into a positionin which a straight section of the strand 35 is pressed against the foil31 in a depression of the conveyor belt 30. Thereafter, the two upperrollers 29a are moved against each other, so that the depression isclosed as illustrated in FIG. 36. At this moment the hexagonal strand iscut into respective bundles 33, and by rotating the rollers 29 the foil31 is wrapped around the bundle. In the next step, the foil 31, ifdesired, can be welded or shrinked against the bundle. The rollers 29aare then moved away from one another, and the packed in hollow fiberbundle 33, 31 is discharged. Preferably, the device 29, 30 is assignedto each side of the hexagonal strand, that is, altogether six hexagonaldevices are employed opposite the sides of the hexagonal strand and areoperated simultaneously. If however only a single device 30, 29 is usedas shown in FIG. 33, the aforedescribed steps must be consecutivelyexecuted six times, and non-illustrated clamping means must be used tohold the strand in position in the slots 28 so long until all sides ofthe strand are processed.

As mentioned before, the devices of FIGS. 15-17 and 33-36 areparticularly advantageous for producing bundles of freshly spun andundulated hollow fibers made by the regeneration of cellulose from acuprammonium solution, whereby the resulting hollow fiber bundleexhibits an excellent urea-clearance effect. Accordingly, such hollowfiber bundles are particularly suitable for blood dialysis. It will benoted that for the first time freshly spun hollow fibers of theaforedescribed types can be directly and continuously processed inbundles which meet all standard requirements.

Very good results have been obtained when the method of this invention,in using the devices of FIGS. 15-17 and 33-36, is also applied to hollowfilaments made of porous polypropylene, whereby the dimensions of thefibers are in the aforementioned ranges. Such porous hollow fibers ofpolypropylene and their methods of production are described for examplein the German patent publication No 2,833,493.

It will also be noted that the method of this invention and thecorresponding devices for carrying out this method is suitable forproducing bundles of hollow fibers having most diversified dimensions oftheir diameters or wall thicknesses.

Tests have been made also with hollow fibers made of other materialsthan the described polymer fibers with conventional dimensions, and ithas been found that the method and devices of this invention present nolimitations as far as the material of the fibers is concerned.

FIG. 37 shows a cut away section of a hollow fiber bundle made ofzig-zag waved fibers 3. In a typical bundle of this kind, there areemployed several hundred hollow fibers, for example. In this example thewaving of individual fibers has the same phase, that is the valleys andthe crests of the waves coincide with each other. In general, however,the waving of the fibers is shifted, whereby the planes of the waves areoriented at random.

FIG. 38 shows an example of a bundle composed of hollow fibers 3undulated in a sinusoidal waveform and being arranged in mutuallyshifted positions in which the wave valleys and crests of individualfibers do not coincide with each other. The bundles of this type containagain several hundred or several thousand individual fibers 3.

FIG. 39 shows by way of an example an arrangement of differentlyundulated hollow fibers of different shapes and wavelengths, as well asof different dimensions and orientations. It will be seen that some ofthe fibers are undulated in a zig-zag shape, whereas other fibers have asinusoidal configuration oriented in different planes. The resultingbundle has a particularly loose or slack quality.

FIG. 40 illustrates a bundle composed of zig-zag undulated fibers aswell as of straight fibers. It has been found that, in order to achievea loose bundle, it is sufficient when only a portion of the fibers inthe bundle undergo an undulation.

FIG. 41 shows an embodiment of a fiber guiding device in which thehollow fiber 3 is guided past guiding rollers 38 arranged on the rotaryarm 27.

FIG. 42 shows a modification of the fiber guiding device 1, in which therotary arm is in the form of a tube 39.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above.

While the invention has been illustrated and described as embodied inspecific examples of the method and devices for producing bundles ofhollow fibers, it is not intended to be limited to the details shown,since various modifications and structural changes may be made withoutdeparting in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapted for various applications without omitting features that,from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.
 1. A method of producing bundles ofhollow fibers, comprising the steps of(a) placing at least one pair ofstationary take-up elements in a working position and simultaneouslyplacing at least a second pair of stationary take-up elements in a readyposition; (b) winding at least one continuous hollow fiber about the onepair of stationary take-up elements in the working position so as tocreate thereon a strand of hollow fibers of a desired thickness; (c)moving said one pair together with the strand away from said workingposition and simultaneously placing said second pair of stationarytake-up elements from the ready position into the working position tostart winding of another strand thereon without interrupting the hollowfiber; (d) then cutting the completed strand into bundles while windingthe other strand about the second pair of stationary take-up elements;and (e) repeating the steps (c) and (d) with the second pair.
 2. Amethod as defined in claim 1, wherein the hollow fiber is a freshly spunfiber continuously fed to said working position.
 3. A method as definedin claim 1, wherein a plurality of stationary take-up elements is placedin said working position so as to wind a polygonal strand of hollowfibers thereon.
 4. A method as defined in claim 3, wherein said take-upelements are arranged in the form of an irregular polygon havingdifferent side lengths.
 5. A method as defined in claim 4, wherein thesides of the polygonal strand are cut into bundles of different lengths.6. A method as defined in claim 1, wherein the continuous hollow fiberis undulated and fixed to obtain a permanent waveform.
 7. A method asdefined in claim 6, wherein the undulation and fixation of the fiber isperformed before its winding on the take-up elements.
 8. A method asdefined in claim 6, wherein the undulation and fixation of the waveformof the hollow fiber is performed after the cutting of the strand ofhollow fibers.
 9. A method as defined in claim 1, wherein the processingof the completed strand of hollow fibers includes the application ofwrapping means around a portion of the strand prior to the cutting ofthe latter.
 10. A method as defined in claim 9, wherein the wrappingmeans is a wrapping foil which is first applied against a portion of thestrand and after the cutting of the strand into the bundles the foil iswound in several layers around the bundle.
 11. A method as defined inclaim 6, wherein the continuous hollow fiber is undulated in acirculating form and fixed to a permanent waveform in this form.
 12. Amethod as defined in claim 11, wherein the fiber has a uniform waveform.13. A method as defined in claim 11, wherein the fiber has a uniformzig-zag form.
 14. A method as defined in claim 11, wherein the fiber hasa helical waveform.
 15. A method as defined in claim 6, wherein theundulated hollow fibers are arranged in the produced bundles with amutual phase shift.
 16. A method as defined in claim 6, wherein aplurality of differently waved fibers is simultaneously wound around thetake-up elements to form the strands and bundles.
 17. A method asdefined in claim 1, wherein the continuous hollow fiber is produced byregenerated of cellulose from a cuprammonium cellulose solution.
 18. Amethod as defined in claim 17, wherein the inner diameter of the hollowfiber is in the range of between 100 and 300 microns and the wallthickness of the fibers is between 3 and 20 microns.
 19. A method asdefined in claim 1, wherein the hollow fiber is made of a porouspolypropylene.
 20. A method as defined in claim 19, wherein the innerdiameter of the fiber is between 200 and 2000 microns, and the wallthickness is between 50 and 400 microns.
 21. A method as defined inclaim 6, wherein the undulation of the hollow fiber is fixed by theapplication of heat.
 22. A method as defined in claim 6, wherein theundulation of the hollow fiber is fixed by the application of moistureand heat.
 23. A method as defined in claim 1, wherein said take-upelements in the working position are arranged in a substantiallyhorizontal plane.
 24. A method as defined in claim 1, wherein theembracing of the strand prior to its cutting, the cutting of the strandinto the bundles, and the packing of respective bundles are performed byan automatic machine.